In lithography, there is an ongoing desire to reduce the size of features in a lithographic pattern to increase the density of features on a given substrate area. In photolithography, the push for smaller features has resulted in the development of technologies such as immersion lithography and extreme ultraviolet (EUV) lithography, which are somewhat costly.
A potentially less costly road to smaller features that has gained increasing interest is so-called imprint lithography, which generally involves the use of a “stamp” to transfer a pattern onto a substrate. One feature of imprint lithography is that the resolution of the features is not limited by, for example, the wavelength of a radiation source or the numerical aperture of a projection system as in photolithography, but may be limited by the pattern density on the stamp (also referred to as template). There are three main approaches to imprint lithography, examples of which are schematically depicted in FIGS. 1a to 1c. 
FIG. 1a shows an example of a type of imprint lithography that is often referred to as micro-contact printing. Micro-contact printing involves transferring a layer of molecules 11 (typically an ink such as a thiol) from a template 10 (e.g. a polydimethylsiloxane template) onto a resist layer 13 which is supported by a substrate 12 and planarization and transfer layer 12′. The template 10 has a pattern of features on its surface, the molecular layer being disposed upon the features. When the template is pressed against the resist layer, the layer of molecules 11 are transferred onto the resist. After removal of the template, the resist is etched such that the areas of the resist not covered by the transferred molecular layer are etched down to the substrate. For more information on micro-contact printing, see e.g., U.S. Pat. No. 6,180,239.
FIG. 1b shows an example of so-called hot imprint lithography (or hot embossing). In a typical hot imprint process, a template 14 is imprinted into a thermosetting or a thermoplastic polymer resin 15, which has been cast on the surface of a substrate 12. The resin may, for example, be spin coated and baked onto the substrate surface or, as in the example illustrated, onto a planarization and transfer layer 12′. When a thermosetting polymer resin is used, the resin is heated to a temperature such that, upon contact with the template, the resin is sufficiently flowable to flow into the pattern features defined on the template. The temperature of the resin is then increased to thermally cure (crosslink) the resin so that it solidifies and irreversibly adopts the desired pattern. The template may then be removed and the patterned resin cooled. In hot imprint lithography employing a layer of thermoplastic polymer resin, the thermoplastic resin is heated so that it is in a freely flowable state immediately prior to imprinting with the template. The thermoplastic resins may be heated to temperatures considerably above the glass transition temperature of the resin. The template is pressed into the flowable resin and then cooled to below its glass transition temperature with the template in place to harden the pattern. Thereafter, the template is removed. The pattern will consist of the features in relief from a residual layer of the resin which may then be removed by an appropriate etch process to leave only the pattern features. Examples of thermoplastic polymer resins used in hot imprint lithography processes are poly (methyl methacrylate), polystyrene, poly (benzyl methacrylate) or poly (cyclohexyl methacrylate). For more information on hot imprint, see e.g., U.S. Pat. No. 4,731,155 and U.S. Pat. No. 5,772,905.
FIG. 1c shows an example of UV imprint lithography, which involves the use of a transparent template and a UV-curable liquid as resist (the term “UV” is used here for convenience but should be interpreted as including any suitable actinic radiation for curing the resist). UV curable liquids are often less viscous than the thermosetting and thermoplastic resins used in hot imprint lithography and consequently may move much faster to fill template pattern features. A quartz template 16 is applied to a UV-curable resin 17 in a similar manner to the process of FIG. 1b. However, instead of using heat or temperature cycling as in hot imprint, the pattern is frozen by curing the resin with UV light that is applied through the quartz template onto the resin. After removal of the template, the resist is etched such that the areas of the resist not covered by the transferred molecular layer are etched down to the substrate. A particular manner of patterning a substrate through UV imprint lithography is so-called step and flash imprint lithography (SFIL), which may be used to pattern a substrate in small steps in a similar manner to optical steppers conventionally used in IC manufacture. For more information on UV imprint, see e.g., U.S. Published Application No. 2004-0124566, U.S. Pat. No. 6,334,960, PCT Publication No. WO 02/067055, and the article by J. Haisma entitled “Mold-assisted nanolithography: A process for reliable pattern replication”, J. Vac. Sci. Technol. B14(6), November/December 1996.
Combinations of the above imprint techniques are also possible. See, e.g., US Published Application No. 2005-0274693, which mentions a combination of heating and UV curing a resist.
Once an imprintable medium, such as the thermosetting/thermoplastic polymer resin 15 or UV-curable resin 17, has been imprinted, the template has to be released from the medium without damaging the imprinted pattern. Damage can be caused by introduction of stresses within the medium which exceed the strength of the medium. For example, when the direction of the force acting on the template to release it from the medium is not perfectly perpendicular to the surface of the imprinted medium, which is often the case, the template moves sideways, which can damage the cast structures of the imprinted pattern.
FIG. 2a illustrates an idealized mechanism for the release of an imprint template 20 from a patterned imprintable medium 21 supported on a substrate 22. The template 20 is linearly displaced along an imprint axis 23 by an imprint actuator 24 so as to bring the template 20 into contact with the medium 21 to imprint a predetermined pattern and subsequently release the template 20 from the medium 21 in the direction of arrow A. In the idealized situation depicted in FIG. 2, imprint axis 23 is perpendicular to a patterned surface 25 of the medium 21 such that release of the template 20 from the medium 21 does not cause any damage to the cast structures 26 of the patterned medium 21.
FIG. 2b depicts the practical mechanism of release of the template 20 from the imprintable medium 21. Typically, in practice, the imprint actuator 24 will not be able to displace the template 20 perfectly linearly along the imprint axis 23 during release of the template 20 from the medium 21. Instead, the actuator 24 will generally displace the template 20 along a release axis 27 which is angularly offset with respect to the imprint axis 23. Consequently, sideways displacement of the template 20 will occur and the template 20 will move in the direction of arrow B during release from the medium 21. Since the template 20 is no longer displaced perpendicularly with respect to the patterned surface 25 of the medium 21, the cast structures 26 of the patterned medium 21 may be damaged.
It is desirable to provide, for example, an imprint lithography apparatus and method which overcome or mitigate a problem associated with the art.